Republicans in Congress are pressing Secretary of State Rex Tillerson to change his tune on the Iran deal. They want him not to certify that Iran is complying with the nuclear deal it struck with the United States and five other nations, which could pave the way for Congress restoring various sanctions.

Four leading GOP senators wrote to Tillerson on Tuesday about the Iran deal, which he is required by law to weigh in on every 90 days. In April, Tillerson disagreed with other Trump administration officials and decided to certify that Iran was in compliance with the Joint Comprehensive Plan of Action and that sanctions relief was in the national security interest of the United States.

At the time, Tillerson wrote to House Speaker Paul D. Ryan (R-Wis.) to say he still believed that “Iran remains a leading state sponsor of terror, through many platforms and methods,” but said that the Trump administration was in the middle of its Iran policy review and therefore was not ready to make any big changes to their approach.

Now, three months later, GOP senators are losing patience and want Tillerson to call out Iran for alleged violations of the deal and other assorted mischief, whether the administration’s internal policy review is completed or not.

“We believe that a change in that policy is long overdue,” wrote Sens. Tom Cotton (R-Ark.), Ted Cruz (R-Tex.), David Perdue (R-Ga.) and Marco Rubio (R-Fla.). “As we near the end of another 90-day review period, U.S. interests would be best served by a sober accounting of Iran’s JCPOA violations as well as the regime’s aggressive and destabilizing behavior.”

Their letter goes through a long list of Iran’s alleged skirting of the terms of the deal and other instances of Iran’s behavior the senators believe run counter to the deal’s core objective, which is to prevent Iran from obtaining a nuclear weapon.

A law passed by Congress in 2015 called the Iran Nuclear Agreement Review Act requires the secretary of state to certify every 90 days that Iran is in compliance with the nuclear deal and that U.S. sanctions relief for Iran is in the national interest. The senators argue that the national interest requires more pressure on Iran now.

“Iran continues to wage a campaign of regional aggression, sponsor international terrorism, develop ballistic missile technology, and oppress the Iranian people. Iran’s aggression directly targets the United States,” the letter states. “In light of these actions, there is simply no basis on which to make a certification that U.S. national security is bolstered by continued sanctions relief. In fact, a continuation of current policy would be tantamount to rewarding Iran’s belligerence.”

If Tillerson decided not to certify Iran’s compliance with the nuclear deal, some warn that the deal itself could unravel as both Iran and America’s partners in the P5+1 group could conclude that the U.S. was backing away from it. Congressional officials said that under the law, the deal would not necessarily collapse. Congress could then choose to restore sanctions or Congress could take no action whatsoever. The credible threat of more sanctions could be used as leverage for the Trump administration in dealings with Tehran, the argument goes.

President Trump has called the Iran deal “the worst deal ever negotiated,” and one that is “catastrophic for America, for Israel and for the whole of the Middle East,” but he has taken no action to renegotiate or terminate the deal. The National Security Council led interagency Iran policy review is still ongoing.

Trump spoke with Cotton last week about the letter and Trump again stressed how bad he thinks the deal is, a spokesperson for Cotton told me. Congress and the president are losing patience on the issue and a tougher stance on Iran’s nuclear-related activities could be coming soon, whether Tillerson makes this certification or not.